Indicating fuse plug



March 4, 1924.

.L E. JOHNSON INDICATING FUSE PLUG Filed Nov. 27. 1920 Patented Mar. 4, 1924,

UNITED STATES PATENT OFFICE.

JOHN n .ronnson, or on mm, rumors, assren'on or ens-mar r 0. nnwann LINDGBEN, or nu ma, rumors.

INDIOATING FUSE PLUG.

Application flied November 27, 1980. Serial No. 428,794.

To all whom it may concern.

Be it known that I, JOHN E. Jormsox, citizen of the United States, residing at De Kalb, Illinois, have invented certain new and useful Improvements in an Indicating Fuse Plug; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it general object being t up rtains to make and use the same.

y invention relates to fusible devices as used for protecting electric circuits, its

at of providin simple, effective and inexpensive means or indicating when the fuse in the device has blown. More particularly, my invention relates to electric fuse plugs and aims to rovide sim 1e and inexpensive means for instantly a ording a visual indication of the blowing of the fuse within a plug, so that the burnt out fuse plugs can readily be detected without the necessity of previously handling or testing the same. Furthermore, I aim to provide indicatin means which can readily be adopted in t e construction of standard types of fuse plugs, and to arrange these in such a manner that they will not in any way interfere with the fuse plug either as to its installation or otherwise. Still further and more detailed objects will a ar from the following specification and rom the accompanying drawings, in which a ig. 1 is a central and longitudinal section through a fuse plug embodying my in-.

vention and showing the same with the fuse intact.

Fig. 2 is a plan view of the same taken after the indicating film has been ruptured by the burning of the fuse.

Fig. 3 is a transverse section through the plug of Fig. 1, taken from the lower surace of the opaque indicating film.

Fig. 4 is a section similar to the upper portion of Fig. 1, but taken after the fuse as blown.

In the embodiment of the drawings, I ani showing my invention as applied to a fusible device of the ty popularly known as a fuse plug and a apted for insertion in a receptacle of the screw-shell type. This fuse plug has a hollow porcelain bod 1 carrymg an axially disposed termlna 2 and also 'carryin a perip oral and spiially grooved termma 3. The porcelain y 1 has a chamber 4 open at the rear end of the plug and housin a fuse 5 which has its ends respectivel sol ered to the terminals 2 and 3. This use is desirably bowed so as to present a bend or bight directed towards the cap of the plug, and this cap desirably includes a substantially transparent mica lisk76 clamped in position by a metal col- Thus arranged, the fuse can ordinarilybe seen more or less distinctly through the cap 6, depending both on the transparency of the mica and the li hting available. However, the clearness wit WhlCh the fuse may be viewed through the cover is not always adequate for determining whether or not the fuse is still in operative condition, so that a visual inspection is not ample for this purpose but in a large share of cases has to be supplemented b a removal and testing of the fuse plug. onsequently, the electrician whowants to locate a burnt-out fuse in a cabinet containing a group of such fuse plugs is obliged to remove and test one after another of the plugs before he finds the one containing the ruptured fuse. This consumes valuable time and also is difficult for the ordinar user who has no facilities for testing such plugs.

To avoid such a loss of time, as well as the delay and expense in attending to the same, I provide a screen which is normally intact butwhich is adapted to be ruptured by the heat of the blowin fuse, so that the im erfect condition of ghis screen will instant y indicate that it is in a plu in which a fuse has blown. Moreover, desirably emplo for this purpose a screen which norma ly conceals the interior of the chamber 4 entirely from view and which readily reflects exterior li ht, so as to increase the visual difference tween the normal screen and a in tured one. If this screen touched the mica cap, such contact might cool the heated screen sufiicientl to interfere with an adequate rupturing o the film by theheat of the blowing fuse, hence I desirably space the screen from the mica cap.

To accomplish these purposes at a trifling addition in the cost of construction over the ordinary fuse plug of this t pe, I place a disk 8 of a suitable thermal y ru turable material over the mouth of t body 1 of the plug, before slipping the "sequently, the screen which normally presents a uniformly opaque face towards the mica cover 6 will appear punctured after the manner of Fig. 2 when the fuse has blown, thereby instantly indicating wh ch one of a group of plugs is no longer In operative condition.

To make this visual indication all the more clearly apparent, I desirably employ a screen. having a good reflecting surface on the side towards the mica. Such a refleeting surface may be afforded either by the metal of the foil itself, or by a glossy colored coating on the latter after the manner commonly used on the foils emplo ed over the stoppers of bottles. Since suci a polished film readily reflects light, the difference between the light thus reflected by the remaining portion of a punctured film and the necessarily darkened interior of the chamber 4 will be all the greater, as indicated in Fig. 2 of the drawings, thus increasing the readiness with which the spoilt fuse plug can be detected.

To insure an instantaneous rupturing of such an opaque film, I desirably bring the fuse fairly close to the latter, and I may further increase the certainty of action by employing a fuse having a portion 10 of reduced cross section adjacent to the screen or film, so as to cause the fuse to blow at a point so close to the'film that the heat of the blowing will be sure to melt a portion of the screen. In practice, the resulting rupture may also be assisted by the explosive action of the metal of the ruptured However, while I have illustrated and described my invention as embodied in a highl desirable form in which the rupturab e screen is in the shape of a disk and is made of a metal foil, and in which this screen is spaced by an annular washer from the cover of a fuse lug of the screw type, I do not wish to be limited to these or other details of the construction and arrangement here disclosed, since numerous variations might obviously be made without departing from the spirit of my invention or from the ap nded claims.

claim as my invention 1. A fuse plug having a cavity therein, a fuse mounted within the cavity, and a metal foil stretched across the mouth of the cavity and clamped substantially at its periphery against the fuse plug.

2. In a fusible lug, a casing adapted to house a fuse and having an aperture, a thermally fusible film spanning the aperture, and a covering of transparent incombustible and infusible material disposed across the aperture outside of the said film.

3. In a fuse plug, a casing housing a fuse a mica disk entirely closing the mouth of the casing, a disk of fusible material disposed between the mica disk and the fuse and spaced from both of the latter and presenting a light-reflecting surface towards the mica disk, and single means for clamping both disks in their said position.

Signed at De Kalb, Illinois, November 24th, 1920.

JOHN E. JOHNSON. 

